Composition based on samarium sesquisulphide, preparation method and use as coloring pigment

ABSTRACT

The composition is based on a samarium sesquisulphide, it exhibits a samarium purity with respect to other rare earth metals of greater than 99% and it comprises at least one alkali metal or alkaline earth metal element, at least a portion of which is included in the crystal lattice of the said sesquisulphide. According to another embodiment, the composition is based on a sesquisulphide of samarium and of at least one rare earth metal which is solely trivalent and it comprises at least one alkali metal or alkaline earth metal element, at least a portion of which is included in the crystal lattice of the said sesquisulphide. According to a third embodiment, the composition exhibits a samarium purity such that the cerium content is less than 1%. The process consists in reacting samarium, trivalent rare earth metal and alkali metal or alkaline earth metal compounds with a gaseous mixture of hydrogen sulphide and of carbon disulphide.

This application is an application under 35 U.S.C. Section 371 ofInternational Application Number PCT/FR98/01775, filed on Aug. 07, 1998.

The present invention relates to a composition based on a samariumsesquisulphide, to its process of preparation and to its use ascolouring pigment.

Inorganic colouring pigments are already widely used in many industries,in particular in those of paints, plastics and ceramics. In suchapplications, the properties, which are, inter alia, thermal and/orchemical stability, dispersibility (ability of the product to dispersecorrectly in a given medium), compatibility with the medium to becoloured, intrinsic colour, colouring power and opacifying power, allconstitute particularly important criteria to be taken intoconsideration in the choice of a suitable pigment.

Unfortunately, the problem is that most of the inorganic pigments whichare suitable for applications such as above and which are actually usedat the present time on an industrial scale generally make use of metals(cadmium, lead, chromium and cobalt in particular) whose use is becomingincreasingly severely regulated, or even banned, by legislation in manycountries, this being on account of their supposed very high toxicity.Mention may thus more particularly be made, as non-limiting examples, ofthe case of yellow pigments of the lead chromate or cadmium sulphidetype.

It is thus seen that there is a great need for novel inorganicsubstitution pigments.

With this aim and according to a first embodiment, the composition ofthe invention is characterized in that it is based on a samariumsesquisulphide, in that it exhibits a samarium purity with respect toother rare earth metals of greater than 99% and in that it comprises atleast one alkali metal or alkaline earth metal element, at least aportion of which is included in the crystal lattice of the saidsesquisulphide.

According to a second embodiment, the composition of the invention ischaracterized in that it is based on a sesquisulphide of samarium and ofat least one rare earth metal which is solely trivalent and in that itcomprises at least one alkali metal or alkaline earth metal element, atleast a portion of which is included in the crystal lattice of the saidsesquisulphide.

According to a third embodiment of the invention, the composition of theinvention is characterized in that it is based on a samariumsesquisulphide, in that it exhibits a samarium purity such that thecerium content is less than 1% and in that it comprises at least onealkali metal or alkaline earth metal element, at least a portion ofwhich is included in the crystal lattice of the said sesquisulphide.

The invention also relates to a process for the preparation of thecomposition according to the first embodiment, this process beingcharacterized in that a samarium compound exhibiting a samarium puritywith respect to other rare earth metals of greater than 99% and at leastone compound of an alkali metal or alkaline earth metal element isreacted with a gaseous mixture of hydrogen sulphide and of carbondisulphide.

The invention also relates to the process for the preparation of acomposition according to the second embodiment, this process beingcharacterized in that a samarium compound, a compound of the trivalentrare earth metal and at least one compound of an alkali metal oralkaline earth metal element are reacted with a gaseous mixture ofhydrogen sulphide and of carbon disulphide.

The invention also relates to a process for the preparation of thecomposition according to the third embodiment, this process beingcharacterized in that a samarium compound exhibiting a samarium puritysuch that the cerium content is less than 1% and at least one compoundof an alkali metal or alkaline earth metal element are reacted with agaseous mixture of hydrogen sulphide and of carbon disulphide.

The compositions of the invention exhibit a strong yellow colour.

Other characteristics, details and advantages of the invention willbecome even more fully apparent on reading the description which followsand the various concrete but non-limiting examples intended toillustrate it.

The composition according to the first embodiment of the invention willnow be described.

This composition is based on a samarium sesquisulphide of formula Sm₂S₃.It is a sesquisulphide of γ type.

One characteristic of the composition according to this first embodimentis the purity of the samarium. The composition must exhibit a samariumpurity, measured with respect to the other rare earth metals, of greaterthan 99%. This purity can be at least 99.5% and more particularly atleast 99.9%.

Here and throughout the description, the purities are given as weight ofoxides of the elements samarium, cerium and other rare earth metals.

Rare earth metal is understood to mean, throughout the description, theelements from the group consisting of yttrium and the elements of thePeriodic Classification with an atomic number of between 57 and 71inclusive.

It is known that samarium, from its preparation and separationprocesses, contains impurities which are essentially other rare earthmetals. Samarium usually exhibits a purity of the order of 98.5%. Such apurity is insufficient in the context of the present invention forproducing a pigment with an improved yellow colour.

The composition of the invention comprises, in addition, an alkali metalor alkaline earth metal element. The alkali metal element can moreparticularly be lithium or sodium. The alkaline earth metal element canmore particularly be strontium or calcium. Of course, the sesquisulphideof the composition of the invention can comprise several alkali metaland/or alkaline earth metal elements and, consequently, everything whichis disclosed subsequently with reference to an alkali metal or analkaline earth metal also applies to the case where several alkalimetals and/or alkaline earth metals are present.

According to another characteristic of the invention, this alkali metalor alkaline earth metal element is at least partly included in thecrystal lattice of the sesquisulphide. According to an alternative form,the alkali metal or alkaline earth metal element is essentially orcompletely included in the crystal lattice.

The sesquisulphide of the composition of the invention can in particularpossess a cubic crystallographic structure of Th₃P₄ type, which exhibitsgaps for cations in the lattice; this lacunary structure can besymbolized by giving the sesquisulphides the formulaM_(10.66)[]_(1.33)S₁₆.

According to the invention, one or more alkali metal or alkaline earthmetal elements can be introduced into these cationic gaps, up tosaturation or otherwise of the latter. The presence of these elementswithin the sesquisulphide can be demonstrated by simple chemicalanalysis. Moreover, X-ray diffraction analyses show that the Th₃P₄crystalline phase of the sesquisulphide is retained with, in some cases,modification of the unit cell parameters to a greater or lesser extent,depending both on the nature and on the amount of the alkali metal oralkaline earth metal element introduced.

The composition according to the second embodiment of the invention isbased on a sesquisulphide of samarium and of at least one other solelytrivalent rare earth metal. Solely trivalent rare earth metal isunderstood to mean a rare earth metal which can only exhibit this onevalency and thus a rare earth metal which cannot change to the di- ortetravalent state. Mention may be made, by way of example of such asolely trivalent rare earth metal, of lanthanum, gadolinium ordysprosium.

The trivalent rare earth metal/trivalent rare earth metal and samariumatomic ratio can vary within a wide range. It is generally above 90%.This ratio can more particularly be at most 50%.

The composition according to this second embodiment can furthermore beprepared from a samarium exhibiting the purity mentioned in thedescription of the first embodiment.

For the third embodiment of the invention, the characteristic of thecomposition of the invention lies in the purity of the samarium withrespect to cerium. As indicated above, the cerium content must be lessthan 1%.

Everything which has been disclosed above for the first embodiment asregards the structure of the sesquisulphide, the alkali metal oralkaline earth metal elements and their inclusion in the crystal latticeof the sesquisulphide also applies to the second embodiment and to thethird embodiment.

Generally, the amount of alkali metal element is at most 30% of theatomic amount of all the rare earth metals of the sesquisulphide(samarium, trivalent rare earth metal and other rare earth metals) andpreferably at most 20%. This amount is preferably at least equal to0.1%.

The amount of alkaline earth metal element is at most 50%, expressed asabove.

Alternative forms which relate to the various embodiments of theinvention will now be described.

The compositions of the invention can exhibit a specific particle size.Thus, they can be based on a sesquisulphide which is essentiallycomposed of whole grains with a mean size of at most 1.5 microns, moreparticularly of at most 1 micron. Whole grain is understood to mean agrain which has not been broken or crushed. This is because grains canbe crushed or broken during milling. Scanning electron microscopy photosmake it possible to show that the grains have not been crushed. Itshould also be noted that the sesquisulphide of the composition of theinvention can be deagglomerated, that is to say that, if it is notprovided directly in the form of whole grains, it can be provided in theform of agglomerates which can be composed of agglomerated and/orslightly sintered grains which can give the whole grains bydeagglomeration under mild conditions. Furthermore, the whole grains canbe monocrystalline grains.

As regards more specifically the particle size of the compositions ofthe invention, the latter usually exhibit a mean particle size generallyof less than 2 μm, more particularly of between 0.7 and 1.5 μm. Afterdeagglomeration under mild conditions, the abovementioned grains can beobtained, the mean size of which can be at most 1.5 μm andadvantageously between 0.6 and 0.8 μm. The size of the particles ismeasured by the laser diffraction technique using a particle sizer ofthe Cilas HR 850 (distribution by volume) type.

According to another alternative form, the composition of the inventioncomprises, at the surface of the particles or of the grains whichconstitute it, a layer based on at least one transparent oxide.Reference may be made, as regards a product of this type comprising sucha layer, to European Patent Application EP-A-620,254 on behalf of theApplicant Company, the teaching of which is incorporated here.

This peripheral layer coating the support may not be perfectlycontinuous or homogeneous. However, preferably, the compositionsaccording to this alternative form comprise a transparent oxide coatinglayer which is uniform and of controlled thickness and which does notdetrimentally affect the original colour of the composition beforecoating.

Transparent oxide is understood to mean, in this instance, an oxidewhich, once deposited on the particle or the grain in the form of a moreor less fine film, only absorbs light rays in the visible region to avery small extent or not at all and which does not mask, or only veryslightly masks, the original intrinsic colour of the particle or grain.In addition, it should be noted that the term oxide, which is used forconvenience throughout the present description relating to thisalternative form, should be understood as also covering oxides of thehydrated type.

These oxides, or hydrated oxides, can be amorphous and/or crystalline.

Mention may more particularly be made, as examples of such oxides, ofsilicon oxide (silica), aluminium oxide (alumina), zirconium oxide(zirconia), titanium oxide, zirconium silicate ZrSiO₄ (zircon) and rareearth metal oxides. According to a preferred alternative form, thecoating layer is based on silica. More advantageously still, this layeris essentially, and preferably solely, composed of silica.

According to another alternative form, the composition can comprisefluorine atoms.

In this case, reference may also be made, as regards the arrangement ofthe fluorine atoms, to European Patent Application EP-A-628,608 onbehalf of the Applicant Company, the teaching of which is incorporatedhere.

The fluorinated compositions can exhibit at least one of the followingcharacteristics:

the fluorine atoms are distributed along a concentration gradientdecreasing from the surface to the core of the particles or grainsconstituting the said compositions,

the fluorine atoms are mainly distributed at the outer periphery of theparticles or grains constituting the compositions. Outer periphery isunderstood to mean, in this instance, a thickness of material, measuredfrom the surface of the particle, of the order of a few hundredangstroms. In addition, mainly is understood to mean that more than 50%of the fluorine atoms present in the sesquisulphide are found in thesaid outer periphery,

the percentage by weight of fluorine atoms resent in the compositionsdoes not exceed 10% and referably 5%,

the fluorine atoms are present in the form of fluorinated orsulphofluorinated compounds, in particular in the form of rare earthmetal fluorides or of rare earth metal sulphofluorides (thiofluorides).

According to another alternative form, the compositions of the inventioncan additionally comprise a zinc compound, it being possible for thiszinc compound to be more particularly deposited at the surface of theparticles or grains constituting these compositions. Reference may bemade, for this alternative form, to French Patent ApplicationFR-A-2,741,629 on behalf of the Applicant Company, the teaching of whichis incorporated here.

This zinc compound can be obtained by reaction of a zinc precursor withaqueous ammonia and/or an ammonium salt. The form under which this zinccompound exists in the composition is not known exactly. However, insome cases, it may be thought that the zinc is present in the form of azinc-ammonia complex of formula Zn(NH₃)_(x)(A)_(y), in which Arepresents an anion, such as OH⁻, Cl⁻, the acetate anion or a mixture ofanions, x is at most equal to 4 and y equal to 2.

Of course, the invention also relates to the combination of thealternative forms which have been described above. Thus, it is possibleto envisage a composition in which the particles or the grains comprisean oxide layer with, in addition, fluorine atoms, it being possible forthese compositions additionally to comprise zinc. In particular, forcompositions comprising an oxide layer, the zinc can be included in theoxide layer or situated at the surface of the latter.

The process for the preparation of the compositions of the inventionwill now be disclosed.

The process consists in reacting starting compounds with a gaseousmixture of hydrogen sulphide and of carbon disulphide. In the case ofthe preparation of a composition according to the first embodiment, thesamarium compound is a compound which must exhibit the required samariumpurity, that is to say a purity of greater than 99% and of at least99.5% and more particularly of at least 99.9%, according to the desiredcomposition. In the case of the preparation of a composition accordingto the second embodiment, a compound of the trivalent rare earth metalis used, in addition to a samarium compound. In the case of the thirdembodiment, a samarium compound exhibiting the required cerium content(<1%) is used. In the three cases, use is additionally made of acompound of an alkali metal element and/or of an alkaline earth metalelement.

The samarium and rare earth metal compounds can be oxides or carboxylatecompounds, such as oxalates, acetates, malonates or tartrates. Thealkali metal or alkaline earth metal compounds can be of the same typebut can, in addition, be sulphides or polysulphides, or sulphates.

According to a preferred alternative form, a carbonate or ahydroxycarbonate is used as compound of samarium and optionally of thetrivalent rare earth metal. It is also advantageous to use an alkalimetal or alkaline earth metal carbonate. Such starting compounds make itpossible to obtain compositions with a finer particle size or composedessentially of whole grains as described above. If appropriate, a mixedcarbonate or hydroxycarbonate of samarium and of the trivalent rareearth metal can be employed.

It is also possible to use a samarium and/or rare earth metal carbonateor hydroxycarbonate preimpregnated with an alkali metal or alkalineearth metal element. In this case, an aqueous solution of an alkalimetal or alkaline earth metal salt or hydroxide is formed and thesamarium and/or rare earth metal carbonate or hydroxycarbonate isimpregnated with the solution, then drying is carried out.

The mixture of sulphurizing gas can be employed with an inert gas, suchas argon or nitrogen.

Heating can be carried out at a temperature of between 500 and 1200° C.and more particularly between 600 and 900° C.

The duration of the heating corresponds to the time necessary to obtainthe desired sesquisulphide and this duration decreases as thetemperature increases. By way of example, this duration can range fromapproximately 2 hours for a temperature of 500° C. to approximately 1hour for a temperature of 800° C.

The reaction is generally carried out with a partial pressure of thehydrogen sulphide and of the carbon disulphide which is between 0.1×10⁵and 1×10⁵ Pa.

Finally, the process can be carried out in an open reactor.

The product obtained on conclusion of the heating usually exhibits asuitable particle size for use as pigment. However, if it is desired toobtain a finer particle size, the product can be deagglomerated. Asalready mentioned above, deagglomeration under mild conditions, forexample milling of the air jet type, is sufficient to obtain a mean sizewhich can be less than 1.5 μm and, for example, of at most 1 μm andadvantageously between 0.6 and 0.8 μm.

For the alternative forms which have been disclosed above and for whichthe compositions comprise a transparent oxide, fluorine and/or a zinccompound, these compositions are prepared by employing the processesdisclosed in the abovementioned Patent Applications EP-A-620,254,EP-A-628,608 and FR-A-2,741,629.

In the case of the preparation of a composition comprising a transparentoxide, the process consists essentially in bringing the initialcomposition into contact with a precursor of the abovementionedtransparent oxide and in precipitating the transparent oxide. Initialcomposition is understood to mean, here and in the remainder of thedescription, the composition as obtained following the reaction of thesamarium and optionally trivalent rare earth metal compounds and of thealkali metal or alkaline earth metal compounds with the sulphurizinggaseous mixture and after optional deagglomeration.

Examples of processes will be given below for the various types oftransparent oxides.

In the case of silica, mention may be made of the preparation of silicaby hydrolysis of an alkyl silicate, a reaction mixture being formed bymixing water, alcohol, the composition, which is then suspended, andoptionally a base, an alkali metal fluoride or an ammonium fluoride,which can act as catalyst of the condensation of the silicate. The alkylsilicate is subsequently introduced. It is also possible to carry out apreparation by reaction of the composition, of a silicate, of the alkalimetal silicate type, and of an acid.

In the case of a layer based on alumina, the composition, an aluminateand an acid can be reacted, whereby alumina is precipitated. Thisprecipitation can also be obtained by bringing together and by reactingthe composition, an aluminium salt and a base.

Finally, the alumina can be form ed by hydrolysis of an aluminiumalkoxide.

As regards titanium oxide, it can be precipitated by introducing, intoan aqueous/alcoholic suspension of the composition, a titanium salt,such as TiCl₄, TiOCl₂ or TiOSO₄ on the one hand, and a base, on theother hand. It is also possible to carry out the preparation, forexample, by hydrolysis of an alkyl titanate or precipitation of atitanium sol.

Finally, in the case of a layer based on zirconium oxide, it is possibleto carry out the precipitation by cohydrolysis or coprecipitation of asuspension of the composition in the presence of an organometalliczirconium compound, for example a zirconium alkoxide, such as zirconiumisopropoxide.

The composition comprising fluorine is obtained by subjecting theinitial composition to a fluorination treatment.

This fluorination treatment can be carried out according to anytechnique known per se.

In particular, the fluorinating agent can be liquid, solid or gaseous.Preferably, the fluorination is carried out under treatment conditionswhere the fluorinating agent is liquid or gaseous.

Mention may more particularly be made, as examples of fluorinatingagents which are suitable for the implementation of the treatment, offluorine F₂, alkali metal fluorides, ammonium fluoride, rare gasfluorides, nitrogen fluoride NF₃, boron fluoride BF₃, tetrafluoromethaneor hydrofluoric acid HF.

In the case of a treatment under a fluorinating atmosphere, thefluorinating agent can be used pure or diluted in a neutral gas, forexample nitrogen.

The reaction conditions are preferably chosen such that the saidtreatment only brings about fluorination at the surface of the particlesor grains constituting the composition (mild conditions). In thisrespect, carrying out the fluorination to the core of the particles orgrains does not produce results which are substantially improved withrespect to an essentially surface fluorination. In practice, it ispossible to experimentally monitor and control the degree of progressionof the fluorination reaction, for example by measuring the change in theincrease in mass of the materials (increase in mass brought about by thegradual introduction of fluorine).

The composition comprising zinc can be obtained by bringing together theinitial composition, a zinc precursor and aqueous ammonia and/or anammonium salt. This operation of bringing together makes it possible toprecipitate the zinc compound on the particles or grains constitutingthe composition.

The zinc precursor can be a zinc oxide or hydroxide which is used insuspension. This precursor can also be a zinc salt, preferably a solublesalt. This can be an inorganic acid salt, such as a chloride, or anorganic acid salt, such as an acetate.

Various alternative forms of the process can be envisaged for thepreparation of compositions in which the particles or grains comprisezinc with a layer of oxide and/or of fluorine.

According to a first alternative form, the initial composition, a zincprecursor, aqueous ammonia and/or an ammonium salt and, if appropriate,a precursor of the transparent oxide and a fluorinating agent arebrought into contact and the zinc compound is deposited on the initialcomposition and, if appropriate, the transparent oxide is precipitatedon the said initial composition.

According to a second alternative form, the fluorination treatment iscarried out in a first stage and then, in a second stage, the initialcomposition, thus treated, a zinc precursor, aqueous ammonia and/or anammonium salt and, if appropriate, a precursor of the transparent oxideare brought into contact and the zinc compound is deposited on theinitial composition and, if appropriate, the transparent oxide isprecipitated on the said initial composition.

A third alternative form of the process can also be envisaged. In thiscase, in a first stage, the initial composition, a zinc precursor,aqueous ammonia and/or an ammonium salt and, if appropriate, a precursorof the transparent oxide are brought into contact and the zinc compoundis deposited on the initial composition and, if appropriate, thetransparent oxide is precipitated on the said initial composition, then,in a second stage, the fluorination treatment is carried out.

Another alternative form of the process is also possible. In this case,in a first stage, the initial composition and a precursor of thetransparent oxide are brought into contact and the transparent oxide isprecipitated on the said initial composition, then, in a second stage,the initial composition, thus treated, is brought into contact with azinc precursor, aqueous ammonia and/or an ammonium salt, and the zinccompound is deposited on the initial composition.

In the case of the latter alternative form, the fluorination treatmentcan be carried out during one of the abovementioned stages or before thefirst or after the second.

According to another advantageous alternative form of the process, theoperation of bringing the composition, the zinc precursor, the aqueousammonia and/or the ammonium salt and, if appropriate, the precursor ofthe transparent oxide and the fluorinating agent in contact is carriedout in the presence of an alcohol. The alcohol used is generally chosenfrom aliphatic alcohols, such as, for example, butanol or ethanol. Thealcohol can, in particular, be introduced with the zinc precursor in theform of an alcoholic zinc solution.

According to yet another advantageous alternative form of the process,the composition, the zinc precursor, the aqueous ammonia and/or theammonium salt and, if appropriate, the precursor of the transparentoxide and the fluorinating agent are brought into contact in thepresence of a dispersant. The aim of this dispersant is to prevent theagglomeration of the particles or grains of the composition during theirsuspending for the abovedescribed treatments. It also makes it possibleto operate in more concentrated mixtures. It promotes the formation of ahomogeneous layer of transparent oxide over all the particles.

This dispersant can be chosen from the group of dispersants whichdisperse by a steric effect and in particular non-ionic water-soluble ororganosoluble polymers. Mention may be made, as dispersant, of celluloseand its derivatives, polyacrylamides, poly(ethylene oxide)s,poly(ethylene glycol)s, polyoxyethylenated poly(propylene glycol)s,polyacrylates, polyoxyethylenated alkylphenols, polyoxyethylenated longchain alcohols, poly(vinyl alcohol)s, alkanolamides, dispersants of thepolyvinylpyrrolidone type or compounds based on xanthan gum.

In addition, it should be noted that it can be advantageous to treatwith ultrasound the suspension obtained from the mixture of thereactants.

Finally, the product obtained at the end of the operations describedabove can be washed with water or with alcohol. It can also be dried inthe air or under vacuum.

The invention also relates to the use of a composition according to theinvention as colouring pigment for colouring a material.

This is because the composition of the invention has a good colouringpower and a good covering power and, for this reason, is suitable forthe colouring of numerous materials, such as plastics, paints andothers.

Thus, and more specifically, it can be used in the colouring of polymersfor plastics which can be of the thermoplastic or thermosetting type.

Compositions comprising zinc are very particularly suited forapplications in which they are employed at a relatively high temperatureand under conditions where there is a risk of H₂S being released as aresult, possibly, of a partial hydrolysis of the sulphur-comprisingcompound. More specifically, they can be used in the colouring ofpolymers for plastics which can be of the thermoplastic or thermosettingtype, these polymers being capable of containing traces of water.

Mention may be made, as thermoplastic resins capable of being colouredaccording to the invention, purely by way of illustration, of poly(vinylchloride), poly(vinyl alcohol), polystyrene, styrene-butadiene,styrene-acrylonitrile and acrylonitrile-butadienestyrene (A.B.S.)copolymers, acrylic polymers, in particular poly(methyl methacrylate),polyolefins, such as polyethylene, polypropylene, polybutene orpolymethylpentene, cellular derivatives, such as, for example, celluloseacetate, cellulose acetobutyrate or ethylcellulose, or polyamides,including polyamide-6,6.

As regards the thermosetting resins for which the composition accordingto the invention is also suitable, mention may be made, for example, ofphenoplasts, aminoplasts, in particular ureaformaldehyde ormelamine-formaldehyde copolymers, epoxy resins and thermosettingpolyesters.

The composition of the invention can also be employed in specialpolymers, such as fluorinated polymers, in particularpolytetrafluoroethylene (P.T.F.E.), polycarbonates, silicone elastomersor polyimides.

In this specific application for the colouring of plastics, thecomposition of the invention can be employed directly in the form ofpowders. It is also possible, preferably, to employ it in a predispersedform, for example as a premix with a portion of the resin, or in theform of a concentrated paste or of a liquid, which makes it possible tointroduce it at any stage in the manufacture of the resin.

Thus, the composition according to the invention can be incorporatedinto plastics, such as those mentioned above, in a proportion by weightgenerally ranging either from 0.01 to 5% (relative to the final product)or from 20 to 70%, in the case of a concentrate.

The composition of the invention can also be used in the field of paintsand varnishes and more particularly in the following resins: alkydresins, the most common of which is named glyceryl phthalate resin;resins modified with long or short oil; acrylic resins derived fromesters of acrylic acid (methyl or ethyl) and methacrylic acid,optionally copolymerized with ethyl, 2-ethylhexyl or butylacrylate;vinyl resins, such as, for example, poly(vinyl acetate), poly(vinylchloride), poly(vinyl butyral), poly(vinyl formal), and vinyl chlorideand vinyl acetate or vinylidene chloride copolymers; phenolic oraminoplast resins, generally modified; polyester resins; polyurethaneresins, epoxy resins; or silicone resins.

The composition is generally employed in the proportion of 5 to 30% byweight of the paint and of 0.1 to 5% by weight of the varnish.

In addition, the composition according to the invention is also capableof being suitable for applications in the rubber industry, in particularin floor surfacings, in the paper and printing inks industry, in thefield of cosmetics, and for many other uses, such as, for example, andin a non-limiting manner, dyes, in leathers, for finishing the latter,and laminated coatings for kitchens and other work surfaces, ceramicsand glazes.

The composition of the invention can also be used in the colouring ofmaterials based on or obtained from at least one inorganic binder.

This inorganic binder can be chosen from hydraulic binders, air-curedbinders, plaster and binders of the anhydrous or partially hydratedcalcium sulphate type.

Hydraulic binders is understood to mean substances having the propertyof setting and of hardening after addition of water with the formationof water-insoluble hydrates. The products of the invention apply veryparticularly to the colouring of cements and, of course, of theconcretes manufactured from these cements by addition to the latter ofwater, of sand and/or of gravel.

In the context of the present invention, the cement can be, for example,of the aluminous type. This is understood to mean any cement containinga high proportion either of alumina as such or of aluminate or of both.Mention may be made, as examples, of cements based on calcium aluminate,in particular those of the Secam type.

The cement can also be of the silicate type and more particularly basedon calcium silicate. Examples which may be given are Portland cementsand, in cements of this type, quick-setting or very-quick-settingPortland cements, white cements, those which are resistant to sulphatesand those comprising blast furnace slag and/or fly ash and/ormeta-kaolin.

Mention may also be made of cements based on calcium sulphatehemihydrate and magnesia cements, known as Sorel cements.

The composition of the invention is also used in the colouring ofair-cured binders, that is to say binders which harden in the open airby the action of CO₂, of the calcium or magnesium oxide or hydroxidetype.

Finally, the composition of the invention is used in the colouring ofplaster and binders of the anhydrous or partially hydrated calciumsulphate type (CaSO₄ and CaSO₄.1/2H₂O).

Finally, the invention relates to coloured compositions of a material,in particular of the plastics, paints, varnishes, rubbers, ceramics,glazes, papers, inks, cosmetic products, dyes, leathers or laminatedcoatings type or of the type based on or obtained from at least oneinorganic binder, which comprise a composition according to theinvention as colouring pigment.

Examples will now be given.

In all the examples given below, the following definitions andprocedures apply.

Preparation of the Products

Use is made, as starting material, of 10 g of a samariumhydroxycarbonate or a mixed samarium and trivalent rare earth metalhydroxycarbonate which has been impregnated with a carbonate of thealkali metal element in solution. The amounts of reactants aredetermined as a function of the stoichiometry of the desired finalproduct. The starting material is subsequently brought to 800° C. for 1hour under a continuous stream, at a flow rate of 6 l/h, of a gaseousmixture containing argon, hydrogen sulphide and carbon disulphide (Ar50%, H₂S 20% and CS₂ 30% by volume).

On conclusion of the calcination, the product is deagglomerated undermild conditions using an air jet mill.

Particle Size

The particle size was determined according to the abovementioned Cilastechnique. In addition, it is specified that the measurement was carriedout on a dispersion of the product in a 0.05% by weight aqueous sodiumhexametaphosphate solution which was subjected beforehand to the effectof an ultrasound probe (probe with a tip with a diameter of 13 mm, 20KHz, 120 W) for 3 minutes. Dispersion index is understood to mean theratio:

σ/m=(d ₉₀ −d ₁₀)/2d ₅₀

in which:

d₉₀ is the diameter of the particles for which 90% of the particles havea diameter of less than d₉₀;

d₁₀ is the diameter of the particles for which 10% of the particles havea diameter of less than d₁₀;

d₅₀ is the mean diameter of the particles.

Chromaticity Coordinates

The chromaticity coordinates L*, a* and b* are given here and throughoutthe description in the CIE 1976 system (L*, a* and b*), as defined bythe Commission Internationale d'Eclairage [International Commission onIllumination] and listed in the Recueil des Normes Francaises[Compendium of French Standards] (AFNOR), calorimetric colour No.X08-12, No. X08-14 (1983). They are determined, as regards measurementscarried out on the products and the plastics, by means of a calorimetersold by the company Pacific Scientific. The nature of the illuminant isD₆₅. The observation surface is a circular pellet with a surface area of12.5 cm². The observation conditions correspond to viewing under anaperture angle of 10°. In the measurements given, the specular componentis excluded for the powders and included for the small plates.

R400 and R700 represent the reflectivity at 400 nm and 700 nm under theabovementioned measuring conditions.

Injection Into the Plastic

The product is incorporated into Eltex® PHV 001 reference polypropylenein a rotating vessel in a proportion by weight of 1%. The mixture issubsequently injected at 220° C. using a Kapsa injection mouldingmachine, model Protoject 10/10, with a cycle of 41 s. The mould ismaintained at a temperature of 35° C.

A parallelepipedal double-thickness (2 and 4 mm) test specimen is thusobtained.

The chromaticity coordinates are measured on the thick part of the smallplate and on a white background.

EXAMPLE 1

This example relates to the preparation of a sulphide, γ-Sm₂S₃, dopedwith lithium. The Li/Sm ratio is 0.15 and a samarium hydroxycarbonateobtained from samarium with a purity of 99.9% is used.

The particle size obtained is 0.7 μm (σ/m=1.7).

The chromaticity coordinates, determined in the CIE Lab system, are:

L*/a*/b*/R400/R700=84.7/−2.6/77.2/5.9/82.7.

After injection into polypropylene (pigment content=1%), thechromaticity coordinates become:

L*/a*/b*=84.5/−2.7/78.3.

EXAMPLE 2

This example relates to the preparation of a sulphide, γ-Sm₂S₃, dopedwith sodium. The Na/Sm ratio is 0.2 and a samarium hydroxycarbonateobtained from samarium with a purity of 99.9% is used.

The particle size obtained is 0.6 μm (σ/m=0.5).

The chromaticity coordinates, determined in the CIE Lab system, are:

L*/a*/b*/R400/R700=87.2/−4.1/76.3/5.9/86.4.

After injection into polypropylene (pigment content=1%), thechromaticity coordinates become:

L*/a*/b*=86.9/−4.3/78.8.

EXAMPLE 3

This example relates to the preparation of a sulphide,γ-(Sm_(0.9)La_(0.1))₂S₃, doped with lithium. The Li/Sm ratio is 0.15 anda mixed samarium and lanthanum (90% Sm/10% La) hydroxycarbonate obtainedwith a samarium with a purity of 98.5% is used.

The particle size obtained is 1.1 μm (σ/m=1.7).

The chromaticity coordinates, determined in the CIE Lab system, are:

L*/a*/b*/R400/R700=86.1/−2.9/78.2/5.7/86.9.

After injection into polypropylene (pigment content=1%), thechromaticity coordinates become:

L*/a*/b*=85/−1.4/78.4.

EXAMPLE 4

This example relates to the preparation of a sulphide,γ-(Sm_(0.5)La_(0.5))₂S₃, doped with lithium. The Li/Sm ratio is 0.15 anda mixed samarium and lanthanum (50% Sm/50% La) hydroxycarbonate obtainedfrom samarium with a purity of 99.9% is used.

The particle size obtained is 1.8 μm (σ/m=1.2).

The chromaticity coordinates, determined in the CIE Lab system, are:

L*/a*/b*/R400/R700=86.4/−2.5/76.6/6.2/85.8.

After injection into polypropylene, the chromaticity coordinates become:

L*/a*/b*=85.4/−4/76.1.

The following examples relate to products which have been subjected,after their preparation, to additional treatments in order to obtain alayer of a transparent oxide, in order to introduce zinc and,optionally, fluorine.

The treatment for the deposition of the oxide layer and the introductionof zinc is as follows.

Polyvinylpyrrolidone (PVP) is dissolved in ethanol.

The optionally fluorinated samarium sulphide is added to this solution,followed by the aqueous ammonia solution and finally the zinc precursor.Ethyl silicate is introduced continuously over 2 hours. After the end ofintroduction of the ethyl silicate, maturing is carried out for 2 hours.The particles thus obtained are washed with ethanol by filtration andthen dried at 50° C. for 12 hours.

EXAMPLE 5

This example relates to a γ-Sm₂S₃ doped with sodium (Na/Sm=0.2) withsamarium with a purity of 99.90%.

The reactants are used in the following proportions:

g of product/kg of suspension Samarium sulphide 200 Ethanol (95%) 643Aqueous ammonia (32%) 100 Zinc oxide 20 Ethyl silicate 32 PVP K10(Company Aldrich) 5 Mw = 10,000

The samarium sulphide used is a samarium sulphide with a γ cubicstructure (Th₃P₄) doped with sodium in an Na/Sm atomic ratio of 0.2.This sulphide was fluorinated beforehand in the following way. 10 g ofproduct are introduced into 100 ml of an ammonium fluoride solution (5%by mass with respect to Sm₂S₃).

The pH of the mixture is brought to 8 by addition of an aqueous ammoniasolution and the mixture is left stirring for one hour. The product issubsequently filtered off and then dried in a desiccator under vacuum.

The product thus obtained is treated, by employing the operatingconditions given above, by using aqueous ammonia.

The product obtained exhibits the following chromaticity coordinates:

L*/a*/b*/R400/R700=82/−1.4/71.6/7/76.3

and a particle size of 1.7 μm (σ/m=1.2).

After injection into polypropylene, the chromaticity coordinates become:

L*/a*/b*=83.4/−2.8/77.8.

EXAMPLE 6

This example relates to a sulphide, γ-Sm₂S₃, doped with sodium(Na/Sm=0.2) with samarium with a purity of 99.9%.

The reactants are used in the following proportions:

g of product/kg of suspension Samarium sulphide 200 Ethanol (95%) 643Aqueous ammonia (32%) 100 Zinc oxide 20 Ethyl silicate 32 PVP K10(Company Aldrich) 5 Mw = 10,000

The samarium sulphide used is a samarium sulphide with a γ cubicstructure (Th₃P₄) doped with sodium in an Na/Sm atomic ratio of 0.2.This sulphide was not fluorinated beforehand. The product is treated byemploying the operating conditions given above, aqueous ammonia beingused.

The product obtained exhibits the following chromaticity coordinates:

L*/a*/b*/R400/R700=82.5/−2.2/71.5/6.7/76.7

and a particle size of 1.1 μm (σ/m=1.1).

After injection into polypropylene, the chromaticity coordinates become:

L*/a*/b*=83.1/−1.3/77.8.

What is claimed is:
 1. A yellow samarium sesquisulphide, comprising acrystal lattice comprising samarium and rare earth metals different fromsamarium, the samarium purity being greater than 99% with respect torare earth metals, and comprising at least one alkali metal or alkalineearth metal element, at least a portion of which being included in thecrystal lattice of said sesquisulphide.
 2. A yellow samariumsesquisulphide according to claim 1, wherein the samarium purity is ofat least 99.5%.
 3. A yellow samarium sesquisulphide according to claim2, wherein the samarium purity is of at least 99.9%.
 4. A yellowsamarium sesquisulphide according to claim 1, wherein the alkali metalelement is lithium or sodium.
 5. A yellow samarium sesquisulphideaccording to claim 1, wherein the sesquisulphide is in the form of wholegrains with a mean size of at most 1.5 μm.
 6. A yellow samariumsesquisulphide according to claim 1, being in the form of particleswhose surface has a layer of at least one transparent oxide.
 7. A yellowsamarium sesquisulphide according to claim 6, wherein the transparentoxide is selected from the group consisting of silica, alumina,zirconia, titanium oxide, zircon and rare earth metal oxides.
 8. Ayellow samarium sesquisulphide according to claim 1, further comprisingfluorine atoms, in an amount not exceeding 10% by weight.
 9. A yellowsamarium sesquisulphide according to claim 8, being in the form ofparticles, with a surface and a core, whose surface has a layer of atleast one transparent oxide, wherein the fluorine atoms are distributedalong a decreasing gradient from the surface to the core of theparticles.
 10. A yellow samarium sesquisulphide according to claim 1,being in the form of particles or grains, comprising a zinc compounddeposited at the surface of the particles or grains.
 11. A yellowsamarium sesquisulphide according to claim 10, wherein the zinc compoundis obtained by reaction of a zinc precursor with aqueous ammonia or anammonium salt.
 12. A process for the preparation of a yellow samariumsesquisulphide as defined in claim 1, comprising the steps of: a)reacting a samarium compound having a samarium purity greater than 99%with respect to the rare earth metals and at least one compound of analkali metal or alkaline earth metal element with a gaseous mixture ofhydrogen sulphide and of carbon disulphide, and b) recovering saidyellow samarium sesquisulphide.
 13. A process according to claim 12,wherein the samarium compound is a samarium carbonate or a samariumhydroxycarbonate.
 14. A process for the preparation of a yellow samariumsesquisulphide as defined in claim 6, comprising the steps of: a)contacting said yellow samarium sesquisulphide with a precursor of thetransparent oxide, b) precipitating said transparent oxide, and c)recovering said yellow samarium sesquisulphide.
 15. A process for thepreparation of a yellow samarium sesquisulphide as defined in claim 10,comprising the steps of: a) bringing into contact a yellow samariumsesquisulphide, a zinc precursor and aqueous ammonia or an ammonium, andb) recovering the yellow samarium sesquisulphide in the form ofparticles or grains with a zinc compound deposited at the surface of theparticles or grains.
 16. A process for colouring a material, comprisingthe step of adding to said material a colouring amount of a yellowsamarium sesquisulfide as defined in claim
 1. 17. A material comprisinga yellow samarium sesquisulfide as defined in claim
 1. 18. A materialaccording to claim 17, wherein the material is a plastic, a paint, avarnish, a rubber, a ceramic, a glaze, a paper, an ink, a cosmeticproduct, a dye, a leather, or a laminating coating.
 19. A yellowsamarium sesquisulphide, comprising a crystal lattice, comprisingsamarium, one or more solely trivalent rare earth metals, and at leastone alkali metal or alkaline earth metal element, at least a portion ofsaid alkali metal or alkaline earth metal element being included in thecrystal lattice of said sesquisulphide.
 20. A yellow samariumsesquisulphide according to claim 19, wherein the atomic ratio betweenthe amount of solely trivalent rare earth metals and the sum of theamounts of trivalent solely rare earth metals and samarium is at most90%.
 21. A yellow samarium sesquisulphide according to claim 20, whereinthe atomic ratio between the amount of solely trivalent rare earthmetals and the sum of the amounts of trivalent solely rare earth metalsand samarium atomic ratio is at most 50%.
 22. A yellow samariumsesquisulphide according to claim 19, wherein the trivalent rare earthmetal is lanthanum, gadolinium or dysprosium.
 23. A yellow samariumsesquisulphide according to claim 19, wherein the alkali metal elementis lithium or sodium.
 24. A yellow samarium sesquisulphide according toclaim 19, being in the form of particles whose surface has a layer of atleast one transparent oxide.
 25. A yellow samarium sesquisulphideaccording to claim 19, further comprising fluorine atoms, in an amountnot exceeding 10% by weight.
 26. A yellow samarium sesquisulphideaccording to claim 19, being in the form of particles or grains,comprising a zinc compound deposited at the surface of the particles orgrains.
 27. A process for the preparation of a yellow samariumsesquisulphide as defined in claim 19, comprising the steps of: a)reacting a samarium compound, a compound of the trivalent rare earthmetal and at least one compound of an alkali metal or alkaline earthmetal element with a gaseous mixture of hydrogen sulphide and of carbondisulphide, and b) recovering said yellow samarium sesquisulphide.
 28. Ayellow samarium sesquisulphide, comprising a crystal lattice, comprisingcerium and samarium, whose purity is such that the cerium is present inan amount of less than 1%, and further comprising at least one alkalimetal or alkaline earth metal element, at least a portion of which beingincluded in the crystal lattice of said sesquisulphide.
 29. A yellowsamarium sesquisulphide according to claim 28, wherein the alkali metalelement is lithium or sodium.
 30. A yellow samarium sesquisulphideaccording to claim 28, being in the form of particles whose surface hasa layer of at least one transparent oxide.
 31. A yellow samariumsesquisulphide according to claim 28, further comprising fluorine atoms,in an amount not exceeding 10% by weight.
 32. A yellow samariumsesquisulphide according to claim 28, being in the form of particles orgrains, comprising a zinc compound deposited at the surface of theparticles or grains.
 33. A process for the preparation of a yellowsamarium sesquisulphide as defined in claim 28, comprising the steps of:a) reacting a samarium compound having a cerium content of less than 1%and at least one compound of an alkali metal or alkaline earth metalelement with a gaseous mixture of hydrogen sulphide and of carbondisulphide, and b) recovering said yellow samarium sesquisulphide.